The invention relates to a method for transmission subscriber-specific data by way of a transmission medium according to a transmission principle based on time slot transmission with time slot separation, a method for transmitting subscriber-specific data, each having their application in particular in TDMA/TDD-based (Time Division Multiple Access/Time Division Duplex) telecommunication systems.
In a DECT-based (Digital Enhanced Cordless Telecommunication) telecommunication system subscriber-specific data is transmitted by way of a DECT radio interface. This transmission takes place according to the DECT standard (ETSI EN 300 175-1 . . . 8, V1.9.1, 09/2005) in time slots with time slot separation—in other words according to the TDMA and TDD transmission principle. According to the DECT standard the time slots can also have different formats (different types of time slots). Thus there are half-slot time slots each with a payload data field of 80 bits, full-slot time slots each with a payload data field of 320 bits or double-slot time slots each with a payload data field of 800 bits.
For the transmission of subscriber-specific data by way of the DECT radio interface it is also desirable in some circumstances to use an SB-ADPCM-based (Sub-Band Adaptive Differential Pulse Code Modulation) broadband voice transmission with a payload data rate of 64 kbps (kbits per second) according to the ITU-T G.722 standard instead of the ADPCM-based (Adaptive Differential Pulse Code Modulation) narrow band voice transmission with a payload data rate of 32 kbps according to the ITU-T G.726 standard generally used until now according to the DECT standard, thereby keeping the number of voice concentrations that can be controlled simultaneously by a DECT base station by way of the DECT radio interface constant despite the increased data rate.
In order to set up a 64 kbps voice data connection between two DECT devices in the DECT system, it is possible to use the above-mentioned double-slot time slot according to the current DECT standard. When low-cost slow-hopping radio parts were used for the respective DECT devices, three or even four (depending on the realization) DECT time slots were always required. This means that only four or three simultaneous connections can be set up, representing a significant loss compared with the maximum six connections with the 32 kbps voice data connection.
Alternatively a plurality of full-slot time slots can be combined, which however also reduces the number of simultaneous connections. The problem could also be resolved with greater expenditure using fast-hopping radio parts instead of the slow-hopping radio parts or with better quality modulation methods.
A further option for realizing the 64 kbps voice data connection in the DECT system is based on a known proposal in the form of a white paper by the company Höft & Wessel at the DECT conference, Feb. 11/12, 2003. The proposal involves shortening the double-slot time slot to a fixed length (so-called long slot). The full-slot time slot can also be shortened to a fixed length according to the shortening proposal from Höft & Wessel (so-called short slot).
When subscriber-specific data is transmitted in a DECT-based telecommunication system a fixed time frame is also used, which is divided into a plurality of time slots. If the aim in the DECT system is now to transmit data simultaneously in a combined mode by way of both symmetrical connections and asymmetrical connections, with transmission taking place in a forward and backward direction (transmit and receive direction) at the same data rate in the case of a symmetrical connection, while in the case of an asymmetrical connection the data rates of the two transmission directions are different, a time slot pair is used for the symmetrical connection and a different number of for example at least four time slots of the same type is used for the two transmission directions for the asymmetrical connection.
In the case of the symmetrical connection the transmission times for the two transmission directions are offset by precisely half the length of a time frame. In the case of the asymmetrical connection three time slots of the four time slots are used for one direction and one time slot for the counter direction. The number of time slots is always even and the time slots are preferably disposed in pairs offset by half the length of a time frame in the frame, so that the asymmetrical connections can be combined as efficiently as possible with symmetrical connections.
WLAN-based (Wireless Local Area Network) telecommunication systems according to the IEEE 802.11 standard use a different transmission principle, which is however much less efficient than that of the DECT system.